Post-FBAWTFT, Langdon doesn't lose his memories from the night his brother died, because the rain only washed away BAD memories. When his father, the newspapers, and everyone who was at the gala start saying that Harry died in a tragic car accident, Langdon knows something isn't right. He's the only person who seems to remember that his older brother was killed by a dark monster with shining white eyes. He supposes it's fair that he's the only person who knows how his brother died, since he's the only person who knows his brother was raping and abusing him for years.

Maybe a 5+1 fic about Langdon trying to tell someone (about the abuse, about magic, about Harry's death, etc.) and not being believed, and then the person who finally believes him?